1. Field of the Invention
The field of the invention is that of the simultaneous manufacture of a plurality of magnetic heads on a wafer or slab made of non-magnetic material, designed to be cut out to separate each magnetic head.
Planar magnetic heads are used notably for the writing or reading of magnetic tapes of the type used in tape recorders, video tape recorders etc.
2. Description of the Prior Art
In a first known structure of magnetic heads, a gap 10 is hollowed out in a magnetic substrate 11 with winding 12 (FIG. 1) for writing or reading on a moving magnetic tape 13.
In one method for making this type of structure by which it is possible to work with magnetic tapes of high coercivity, magnetic layers 14, 15 with high magnetization at saturation (MIG heads) are added on to the opposite faces of the gap 10. However, this technology has the drawback of being complicated to implement, of not being entirely satisfactory from the industrial point of view because the plane of deposition of the layers is perpendicular to the plane in which the magnetic tracks 13 run.
Magnetic heads with a plane structure, such as the one shown in FIG. 2, were then developed. According to this new known design, thin layers 16, 17 made of a magnetic material, are added on at the gap 10 in a plane parallel to the plane in which the magnetic track 13 moves. The magnetic layer forming the thin layers 16, 17 is chosen so as to generate a field that is more intense than the field generated by the material of the magnetic substrate 13 with high coercivity. This technology corresponds to a different operation of the heads, which notably has valuable properties at high frequency. An advantageous application concerns rotating heads, making it possible to work at high throughput rates (several tens of Mbits/s).
In planar magnetic heads of this type, it is possible to distinguish, firstly, the macrogap 18 which has a size, for example, of the order of 200 to 300 .mu.m and, secondly, the microgap 10. These dimensions are given as a non-restrictive illustration.
The invention concerns a method for making planar heads of this type.
There is a known method for the batch manufacture of planar heads, as shown in FIG. 3. This method uses a typical slab 30 obtained by being cut out from a ferrite block with a circular cross-section. On its active face, the slab 30 has a plurality of strips 31 made of a non-magnetic material, parallel to one another. These non-magnetic strips are located on top of a cavity 32. The width 33 of each strip 31 corresponds to the macrogap 18 of the planar head shown schematically in FIG. 2. To make the microgaps, a thin layer of magnetic material with a high saturation coefficient is deposited. Finally "bow-ties" 34, 35 are demarcated in the deposit, in the form of thin layers by masking and ion machining operations. The microgaps 36 are finally demarcated between two wings 34, 35 of the "bow-tie" deposits. It is finally possible to cut out the slab 30 along the two perpendicular sets 37, 38 of parallel planes, so as to individually separate each planar head 39.
There are several known methods of implementing this method, notably the one described in the French patent application No. 2 641 111 filed on behalf of the same Applicant. One characteristic of this type of known planar head is that it is made of a slab of magnetic material 30.
An aim of the invention is to provide a method for the fabrication of planar heads in a slab of non-magnetic material, such as silicon, or again Al.sub.2 O.sub.3 TiC, these being indicated as non-restrictive examples.
There is a known method of this type, as described in the French patent application No. 86 14974. However, the slab of non-magnetic material used according to this prior art document has the drawback of forming an obstacle, owing to its thickness, to the crossing of the magnetic radiation between the upper thin layers and the lower gap cores. The invention is aimed at overcoming this drawback.